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Navigator based respiratory gating during acquisition and preparation phases for proton liver spectroscopy at 3T

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Hock, A., Valkovic, L., Boesiger, P., & Henning, A. (2011). Navigator based respiratory gating during acquisition and preparation phases for proton liver spectroscopy at 3T. Poster presented at 28th Annual Scientific Meeting ESMRMB 2011, Leipzig, Germany.

Purpose/Introduction: Proton MR spectroscopy was shown to be suitable for quantification of different lipids and TMA in the human liver but has not yet been recognized as a tool for liver disease diagnostics in the clinical routine. Most severe reasons are B 0 fluctuation and voxel displacement due to breathing of the subject. Therefore, the quality improvement of 1 H liver spectra using real-time navigator based respiratory gating (NG) during acquisition and during preparation phases is demonstrated. Subjects and Methods: After the approval from the local ethics committee, seven volunteers were consecutively measured at 3T (Achieva, Philips Medical Systems) with a 6-element phased array cardiac coil. After applying a survey, a navigator 2 was placed through the right hemi-diaphragm (Fig.1). For accurate localization of the spectroscopy voxel at the end-expiration position, transversal and coronal navigator gated T 2 weighted TSE images were acquired (Fig.1). Standard PRESS (20x20x20mm 3, TR=3000ms, TE=30ms, 64 averages plus 16 averages of unsuppressed water spectra, 1st order FASTERMAP 1 shimming), with CHESS water-suppression (200Hz window) was used for localization. Inner-volume saturation (IVS) was used to minimize the chemical shift dis placement between lipids and water (Fig.1). For comparison, the measurement was done during free breathing: (1) NG during acquisition and preparation phases (1st order FASTERMAP 1-shimming, F 0 determination, receiver gain optimization and water-suppression) (full nav), (2) just NG during acquisition (no prep nav) and (3) no NG (no nav) and then quantified using the ‘liver-6’ setting in LCModel 3. Results: Fig.2 depicts the spectra measured in one volunteer. The quality improvement (FWHM+-SD, SNR+-SD) by adding the navigators can be seen in table 1. Improvement of the spectral quality FWHM SNR no nav 32.6 +- 11.7 14.1 +- 7.7 no prep nav 23.1 +- 4.2 19.3 +- 9.2 full nav 20.6 +- 3.6 20.4 +- 8.4. Discussion/Conclusion: Our study clearly showed that using real-time NG during the measurement (no prep nav) and even more when NG is also used in the preparation phases (full nav) the spectral quality (SNR and FWHM) is improved leading to a more precise metabolite quantification. In addition, by using NG the measurement position is much more accurate, since the measurement is done in the same phase of the breathing cycle. This improves early diagnosis of different liver diseases e.g. tumors. The method is more time demanding than non-gated free breathing, but it is also applicable in non-compliant patients and children.